Field of the Invention
The invention relates to a driver circuit having series-connected high-side and low-side MOS switches (M1, M2) with MOS transistors for driving a load, a temperature-limiting circuit and a current-limiting circuit, which is assigned to one of the two MOS transistors.
The driver circuit under discussion is implemented, for example, using BICDMOS (Bipolar C- and D-MOS) technology and is in particular provided for use in automobile electronics, for example in conjunction with airbag applications. In the driver circuit under discussion, with the series-connected high-side and low-side MOS switches for driving a load, for the purpose of driving the respective MOS transistor, which is implemented, for example, using DMOS technology, it is normal to provide circuits which are equipped with specific safety measures, in particular with a temperature limiter and with a current limiter. While each drive circuit for the respective power transistor is equipped with its own temperature limiter, it is usually only one of these drive circuits which is equipped with a current limiter.
It is often demanded of MOS transistors that they have a turn-on resistance R.sub.ON of the order of magnitude of about 1.5 ohm. In addition, in particular in conjunction with airbag applications in automobile electronics, it is necessary for the turn-on time of the MOS transistors of greater than 2 milliseconds to be ensured during current limiting operation, the current limiter is typically activated at a current load of approximately 2 A, without the temperature limiter being activated, since within this period of time any thermally induced current "toggling" of the driver stage would prevent the controlled switching of the load. In the case of the airbag application in automobile electronics, failing to satisfy this requirement would mean that the explosion of the detonator for the airbag, and hence the controlled triggering of the latter, would be prevented. In addition, in the case of the application in automobile electronics, there is the risk that the car battery is separated from the on-board network in the event of a collision (load dump), as a result of which a voltage pulse of 40 V in the on-board network is caused, which may lead to overloading of at least one MOS switch of the driver circuit under discussion.
A significant aspect of SPT technology is to keep the chip appropriately small, the factor which determines the area primarily is the power loss which has to be coped with in the MOS transistors. This is particularly critical in the case of using DMOS transistors, which already occupy a relatively large chip area.